We propose to investigate the role of wild type (WT) and temperature-sensitive (ts) mutants of simian virus 40 (SV40), canine distemper virus (CDV), mengovirus, and mouse hepatitis virus (MHV), four different neurotropic virus groups, in the production of chronic demyelination in the central nervous system (CNS) of 3 week old weanling golden Syrian hamsters. CDV, MHV, and mengovirus are neurovirulent and SV40 is neurocarcinogenic in these animals after intracerebral injection. We will use a combined in vitro in vivo approach using virus-specific immunofluorescent micromethods, slab polyacrylamide gel electrophoresis, and transmission electron microscopy. Our primary goal is to develop a reproducible animal model for virus-induced demyelination of the CNS. Our proposal is based upon the observations of other investigators that infections of the CNS by mutant (defective) viruses or combinations of different viruses can result in demyelination. We already have at our disposal ts mutants of SV40 and mengovirus. We propose to isolate and characterize ts mutants of CDV and MHV. We will characterize single and mixed infections of WT and ts mutant viruses in vitro using virus-specific immunofluorescence to monitor viral-specific polypeptide and virion formation, slab polyacrylamide gel electrophoresis to monitor both viral RNA and polypeptide synthesis, and transmission electron microscopy to monitor nucleocapsid and virion formation. Single infections of WT and ts mutant viruses and mixed infections using in vitro complementing or interfering combinations of WT and ts mutant viruses will be monitored for neuropathology, identification of infected cell (oligodendrocyte, astrocyte, or neuron), and demyelination after intracerebral injections in hamsters by immunofluorescent, light, and transmission electron microscopy. Rational approaches to the prevention and treatment of human demyelinating diseases may be achieved through the understanding of the molecular mechanisms of viral-induced demyelination.